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Network Working Group
Request for Comments: 1521
Obsoletes: 1341
Category: Standards Track

N. Borenstein
Bellcore
N. Freed
Innosoft
September 1993

### MIME (Multipurpose Internet Mail Extensions) Part One:
Mechanisms for Specifying and Describing
the Format of Internet Message Bodies

### Status of this Memo

This RFC specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards" for the standardization state and status of this protocol. Distribution of this memo is unlimited.

### Abstract

STD 11, RFC 822 defines a message representation protocol which specifies considerable detail about message headers, but which leaves the message content, or message body, as flat ASCII text. This document redefines the format of message bodies to allow multi-part textual and non-textual message bodies to be represented and exchanged without loss of information. This is based on earlier work documented in RFC 934 and STD 11, RFC 1049, but extends and revises that work. Because RFC 822 said so little about message bodies, this document is largely orthogonal to (rather than a revision of) RFC 822.

In particular, this document is designed to provide facilities to include multiple objects in a single message, to represent body text in character sets other than US-ASCII, to represent formatted multi- font text messages, to represent non-textual material such as images and audio fragments, and generally to facilitate later extensions defining new types of Internet mail for use by cooperating mail agents.

This document does NOT extend Internet mail header fields to permit anything other than US-ASCII text data. Such extensions are the subject of a companion document [RFC-1522].

This document is a revision of RFC 1341. Significant differences from RFC 1341 are summarized in Appendix H.

### Table of Contents

1. Introduction
2. Notations, Conventions, and Generic BNF Grammar
3. The MIME-Version Header Field
4. The Content-Type Header Field
5. The Content-Transfer-Encoding Header Field

5.1. Quoted-Printable Content-Transfer-Encoding
5.2. Base64 Content-Transfer-Encoding

6. Additional Content-Header Fields

6.1. Optional Content-ID Header Field
6.2. Optional Content-Description Header Field

7. The Predefined Content-Type Values

7.1 The Text Content-Type

7.1.1. The charset parameter
7.1.2. The Text/plain subtype

7.2. The Multipart Content-Type

7.2.1. Multipart: The common syntax
7.2.2. The Multipart/mixed (primary) subtype
7.2.3. The Multipart/alternative subtype
7.2.4. The Multipart/digest subtype
7.2.5. The Multipart/parallel subtype
7.2.6. Other Multipart subtypes

7.3. The Message Content-Type

7.3.1. The Message/rfc822 (primary) subtype
7.3.2. The Message/Partial subtype
7.3.3. The Message/External-Body subtype

7.3.3.1. The "ftp" and "tftp" access-types
7.3.3.2. The "anon-ftp" access-type
7.3.3.3. The "local-file" and "afs" access-types
7.3.3.4. The "mail-server" access-type
7.3.3.5. Examples and Further Explanations

7.4. The Application Content-Type

7.4.1. The Application/Octet-Stream (primary) subtype
7.4.2. The Application/PostScript subtype
7.4.3. Other Application subtypes

7.5. The Image Content-Type
7.6. The Audio Content-Type
7.7. The Video Content-Type
7.8. Experimental Content-Type Values

8. Summary
9. Security Considerations
10. Authors' Addresses
11. Acknowledgements
Appendix A -- Minimal MIME-Conformance
Appendix B -- General Guidelines For Sending Email Data
Appendix C -- A Complex Multipart Example
Appendix D -- Collected Grammar
Appendix E -- IANA Registration Procedures
Appendix F -- Summary of the Seven Content-types
Appendix G -- Canonical Encoding Model
Appendix H -- Changes from RFC 1341
References

Original text document
Original PostScript document

Next: 1. Introduction

Connected: An Internet Encyclopedia
RFC 1521